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74 Chapter 6. Final State Interactions and the Eikonal Approximation
section was measured in quasi-perpendicular kinematics for ɛ = 2.015 GeV, q = 1.2
GeV/c, and ω = 0.6 GeV.
The same spectroscopic factors for the 1p 3/2 level were adopted as in Table 6.1,
while the factor was kept unity for the deeper lying 1s 1/2 level. It is very apparent
from Fig. 6.9 that a proton ejected from the 1s 1/2 level undergoes stronger final state
distortion than those that are ejected from the 1p 3/2 level. This reflects the fact that
the deeper lying 1s 1/2 nucleons encounter more obstacles in their way to reach the
surface. However, the eikonal picture apparently overestimates this distortion, as
the strength in the 1s 1/2 channel cannot be reproduced entirely, even with unity
spectroscopic factors. It is worth remarking here that the data exhibit a negligible
asymmetry for this 12 C(e, e ′ p) reaction. In contrast, when looking back to Fig. 6.1,
we see that the data there display a substantial asymmetry for the 16 O(e, e ′ p) reaction,
one of many indications that the 12 C and 16 O differ substantially, although
both have a closed shell structure.
At higher missing energies, it can be witnessed that the calculations underestimate
both the data and the RPWIA results; the cross section even falls steeper
then the plane wave solutions do. The fact that there seems to be a much less adequate
description of the deeper lying 1s 1/2 level, is not very surprising. The main
reason for this is that many other processes compete with the proton knockout
process, especially in the 1s 1/2 channel. For instance, two-nucleon knockout reactions
generate part of the missing strength. As it is very difficult to experimentally
disentangle these competing effects, one cannot expect to adequately describe the
A(e, e ′ p)B(1s −1
1/2
) reaction by just taking this exclusive one-nucleon knockout into
account.
The first experiment measuring the induced proton polarization P n on a “heavy”
nucleus (A > 2) was recently reported by Woo et al. [100]. In this 12 C(e, e ′ ⃗p)
experiment the P n was determined at quasifree kinematics for energy and momentum
transfer (ω,q) = (294 MeV, 756 MeV/c), and sampled a missing momentum range
of 0 - 250 MeV/c. The results of these measurements for both knockout from the
1s 1/2 and the 1p 3/2 bound level are shown in Fig. 6.10, along with our theoretical
results. The excellent agreement of the Glauber results with the experimental data
is striking. This comes a bit as a surprise, since one would expect a potential model
to be more adequate to describe reactions in the lower energy regime.
In the following sections we will more closely inspect the Q 2 evolution of various
effects. Special attention will be paid to the differences between the predictions
obtained in the Glauber (RMSGA) and the optical model (OMEA) approach. At
higher energies, potential models do not appear to be appropriate as the NN scattering
process becomes highly inelastic. We remind the reader that global optical
potential fits to elastic proton-nucleus scattering data are not available for proton